1. Field of the Invention
This invention relates to cardiac physiology. More particularly, this invention relates to the evaluation of electrical propagation in the heart.
2. Description of the Related Art
Cardiac arrhythmias such as atrial fibrillation are an important cause of morbidity and death. Commonly assigned U.S. Pat. No. 5,546,951, and U.S. Pat. No. 6,690,963, both issued to Ben Haim and PCT application WO 96/05768, all of which are incorporated herein by reference, disclose methods for sensing an electrical property of heart tissue, for example, local activation time, as a function of the precise location within the heart. Data are acquired with one or more catheters having electrical and location sensors in their distal tips, which are advanced into the heart. Methods of creating a map of the electrical activity of the heart based on these data are disclosed in commonly assigned U.S. Pat. No. 6,226,542, and U.S. Pat. No. 6,301,496, both issued to Reisfeld, which are incorporated herein by reference. As indicated in these patents, location and electrical activity is typically initially measured on about 10 to about 20 points on the interior surface of the heart. These data points are then generally sufficient to generate a preliminary reconstruction or map of the cardiac surface. The preliminary map is often combined with data taken at additional points in order to generate a more comprehensive map of the heart's electrical activity. Indeed, in clinical settings, it is not uncommon to accumulate data at 100 or more sites to generate a detailed, comprehensive map of heart chamber electrical activity. The generated detailed map may then serve as the basis for deciding on a therapeutic course of action, for example, tissue ablation, to alter the propagation of the heart's electrical activity and to restore normal heart rhythm.
Catheters containing position sensors may be used to determine the trajectory of points on the cardiac surface. These trajectories may be used to infer motion characteristics such as the contractility of the tissue. As disclosed in U.S. Pat. No. 5,738,096, issued to Ben Haim, which is incorporated herein in its entirety by reference, maps depicting such motion characteristics may be constructed when the trajectory information is sampled at a sufficient number of points in the heart.
Electrical activity at a point in the heart is typically measured by advancing a multiple-electrode catheter to measure electrical activity at multiple points in the heart chamber simultaneously. A record derived from time varying electrical potentials as measured by one or more electrodes is known as an electrogram. Electrograms may be measured by unipolar or bipolar leads, and are used, e.g., to determine onset of electrical propagation at a point, known as local activation time.
When evaluating the left atrium, catheters, such as basket catheters may be introduced percutaneously via transseptal puncture. The document Consideration Regarding the Technique for Transseptal Left Heart Catheterization, J. Ross. Circulation 10/1966; 34(3):391-9 points out a number of difficulties with this procedure, caused, for example, by lack of tactile appreciation of the movement of the catheter tip. As a result, the structures engaged by the catheter tip are not recognized, and the degree of pressure exerted against them is uncontrolled. For example, undesired contact of the needle with the posterior wall of the left atrium could occur. Moreover, the optimum site for puncture of the septum is influenced by such considerations as right or left atrial enlargement.